Black arm bands will be worn and daily prayer sessions will be held at Rheinmetall Denel Munition (RDM), as investigators try to figure out what caused the deadly blast that killed eight people at the company's Somerset West plant.

"We had no idea what has happened and caused this detonation," said RDM CEO Norbert Schultze after the fatal blast at the R1bn-a-year plant on Monday afternoon.

Out of respect for their families, their names will not be released officially until forensic specialists have identified those caught up in the blast, and this means an agonising wait until Tuesday, at the earliest.

In the meantime, a long row of flowers lined the front wall of the company, which is also next to Macassar, as people paid their respects.

Schultze was speaking after a two-hour briefing with Public Enterprises Minister Pravin Gordhan and Denel board chairperson Monhla Hlahla who visited the plant - which is in Firgrove, between Somerset West and Macassar, east of Cape Town.

The explosion happened at the company's propellant operation, in one of just over 400 buildings on the vast property which serves a global market for munitions propellants.

The propellants are not weapons themselves, but help projectiles move quickly.

It is understood that the blast took place in a structure where final blending of around 600kg of the "doughy" product was taking place. The company operates strict safety policies, not even allowing objects with electro-magnetic fields around the production buildings.

Schultze said that each building has its own health department license, and the two-storey building that blew up was licensed to have 11 people in it. They believe that only eight people were in it at the time of the blast.

The company is a partnership between Rheinmetall and Denel, established in 2008, with Rheinmetall holding a 51% share and Denel being the minority shareholder with 49%.

About 650 of the around 2 200 people the company employs are based at the Somerset West plant.

Gordhan said Denel had benefited from the company's growth as it moved from importing 30% of its materials, to only about 12%, which had created jobs.

He added that the site had been declared safe for investigations, which were conducted by the SA Police Service, the Department of Labour and an independent contractor appointed by the company with the prior approval of Denel.

Gordhan said it was impossible to say yet what had caused the blast and no photographs of the blast site were allowed to be released or published yet because it is on a National Key Point.

"There are various scenarios and the investigation process will explore each possibility," he said.

Schultze said that counselling has been given to staff and families, and that production had started again on Tuesday.

A row of flowers in memory of the eight people who were killed in an explosion at Rheinmetall Denel munition plant next to Macassar. Public Enterprises Minister Pravin #Gordhan is visiting today. @TeamNews24pic.twitter.com/OnuyD3cEuv

A memorial service will be held soon, and the relatives of the deceased are expected to receive positive identification of remains between Tuesday and Friday.

Gordhan and Schultze said the names of the eight people killed would not be released without permission from the families.

Hlahla said the blast came days after Denel and Rheinmetall marked a partnership of 10 years.

"We will come through it together," said Hlahla.

A condolences book at Rheinmetall Denel Munitions is filling up with messages of support for the families, friends and colleagues of eight people who died in a blast at the Somerset West plant on Monday @TeamNews24pic.twitter.com/PmAlZvAkh7

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